The electro-optical printed circuit board technology relates to the production of printed circuit boards which connect electronic, electro-optical and optical components with one another. They contain electrical conductor tracks on the one hand and optical waveguide structures on the other hand.
Optical waveguide structures consist of a plurality of transparent layers, which are usually three layers, made of UV-curing polymer materials with different refractive indexes. As a result of the transparency, the optical waveguide structures cannot be detected by means of image recognition systems during the mounting of the components. A precise alignment of electro-optical components such as LEDs, laser sources, photodiodes or other elements such as optical fibers etc. on the basis of the optical waveguide structures and relative to the optical waveguide structures is not possible because of their transparency. The precise alignment of the individual components relative to one another is mandatorily required however.
A method for producing optical waveguide structures is known from EP 2000837 which comprises a bottom layer (or under-cladding layer), a core layer and a cladding layer (or over-cladding layer). These layers are applied step by step to a substrate, e.g. a glass pane, and are each structured with the help of an exposure mask. In the first step, the bottom layer is applied to the substrate. Then a structuring of the bottom layer occurs with the exposure through a first exposure mask and a removal of the non-exposed sections, with exposed reference marks also being produced from the material of the bottom layer. The reference marks are not visible because the bottom layer is transparent. In order to make them visible, they are covered in the next step with a metal film. For this purpose, the remaining areas of the bottom layer need to be covered and the reference marks are then coated with metal. This occurs in a vacuum chamber by vapor deposition or sputtering. The reference marks are used in the further production of the optical waveguide structures in order to align the exposure masks for structuring the core layer and the cladding layer.
A method for producing passive optical components with optical waveguide structures is known from EP 1120672, where structures are combined with active optical components within an optical element. A bottom layer, a core layer, a metal layer and a cladding layer are applied step by step to a substrate of silicon and are each structured with the help of exposure masks. The core layer and the metal layer are structured jointly with the help of an exposure mask and a respective exposure and removal of the non-exposed sections. Thereafter, the metal layer is removed on those parts of the structured core layer which form the optical waveguide structures, whereas other parts of the structured core layer with the metal layer are not removed and thus form visible adjusting marks. The adjusting marks are used later on in order to connect these passive components with active optical elements which have a structure which is complementary to and corresponds to the adjusting marks.
An optical waveguide structure in which the core layer and the metal-coated reference marks are formed simultaneously is also known from U.S. Pat. No. 6,553,171.